This is my newly created bog garden, while not planted strictly for wildlife I hope the dwarf mint (menthus pulegium, far right) will attract the bees.
The container already had some holes in the bottom, so I lined it with an old compost bag (with plenty of pin holes though to allow some drainage) then filled it with clay soil from the garden and plenty of well rotted manure, and loads of water. Once it had settled after a few days, and I was sure the water wasn't going to leak out, I planted it up with just a few plants, which will spread, and covered it with gravel to help prevent evaporation.